Kinesin's cover-neck bundle folds forward to generate force
Abstract
Each step of the kinesin motor involves a force-generating molecular rearrangement. Although significant progress has been made in elucidating the broad features of the kinesin mechanochemical cycle, molecular details of the force generation mechanism remain a mystery. Recent molecular dynamics simulations have suggested a mechanism in which the forward drive is produced when the N-terminal cover strand forms a β-sheet with the neck linker to yield the cover-neck bundle. We tested this proposal by comparing optical trapping motility measurements of cover strand mutants with the wild-type. Motility data, as well as kinetic analyses, revealed impairment of the force-generating capacity accompanied by a greater load dependence in the mechanochemical cycle. In particular, a mutant with the cover strand deleted functioned only marginally, despite the fact that the cover strand, the N-terminal "dangling end," unlike the neck linker and nucleotide-binding pocket, is not involved with any previously considered energy transduction pathway. Furthermore, a constant assisting load, likely in lieu of a power stroke, was shown to rescue forward motility in the cover strand deletion mutant. Our results support a stepping mechanism driven by dynamic cover-neck bundle formation. They also suggest a strategy to generate motors with altered mechanical characteristics by targeting the force-generating element.
- Publication:
-
Proceedings of the National Academy of Science
- Pub Date:
- December 2008
- DOI:
- 10.1073/pnas.0805147105
- Bibcode:
- 2008PNAS..10519247K
- Keywords:
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- biological motor;
- force generation;
- optical trap;
- power stroke;
- motor protein;
- Biological Sciences:Biophysics